It isn't a big deal at all. Of course the history behind it is very important, don't get me wrong. Just think of it as a mid Summer holiday that brings family and friends together to eat, socialize, and party during a usually beautiful day.
I've been wishing people a happy 4th, but that's just me being nice and sociable. You aren't really obligated to do that. However, you should take advantage of the happy atmosphere surrounding this day: fire the grill up, eat with some buddies, pound a few beers, and watch some fireworks.
It's not like Christmas when you consider the obligation to celebrate, but if you don't at least try to do something today, you're a real sourpuss.